Method of dividing frequency



Ang. 12, 1941I lK. SCH-LESINGER METHOD OF DIVIDING FREQUENCY Filled Nov. 5, 1938 Jn Venop www@ Patented Aug. 12, 1941 UNITED STATES PATENT OFFICE METHOD F DIVIDING FREQUENCY Kurt Schlesinger, Berlin, Germany, assigner to Radioaktiengesellschaft D. S.Loewe, Berlin- Steglitz, Germany, a company of Germany Application November 5, 1938, Serial No. 239,155

i Y In Germany March 22, 1938 Claims.

liable. In thecase of a divider cascade no stage should make an error, even occasionally, in the frequency or in the phase, so that the complete transmission will not be interfered with.

Unfortunately practically all of the connection systems known heretofore fail to comply entirely with these conditions as to reliability. Two faults occur,- the phase error and the frequency 4error.

In the accompanying drawing:

Figure lashows the curve of a controlling oscillation of a frequency divider. Figure 1b shows the curve ofthe oscillation of the controlled system the synchronisation of which is indefinite. Fig. lcshows a curve of al controlled oscillation formed to prevent an incorrect synchronisation. Figure 2 shows the circuit connection of a frequency divider according to the invention.

Figures 3a-3d show the derivation of -the oscillation according to the Figure 1c from the naturalv oscillation of the controlled system as comparedlwith the -controlling oscillation, and

Figi -shows several frequency dividing stages .coupled together.

In `l'igure la'there is shown by a the rapid control oscillation of the frequency f1 and by b `the slow controlled loscillation of the'frequency f2. @i The divide'rratioof -j2:f1`=1 :7.

. On the basis of-Fig. 1 there can now be eX- plained the occurrence A`oi the phase error and `the .frequency error.V `The oscillations S1 andV S7 `of the Figure 1a arelintended to synchronise vresponse of the controlled system has chronologically the same disposal as the sine wave of 'the operated system. Ar`When the sensitivityof period `of the control oscillation. `In a divider ratio there then occurs in certain circumstances an operation by the oscillations n-l and n+1, a synchronised television image, for example, being continuously displaced by of its width. The probability of a jumping about of this kind is naturally al1 the greater, the greater the desired frequency division has been selected to be. Small differences in frequency on the part of the controlled oscillator leadto a continuous operation on the incorrect Wave, immediately they reach an amount of l it It has been attempted to gain freedom from these uncertain factor vby developing two fundamentally different connection systems:

(1) RC systems or RL systems, (2) CL systems.

(1) Systems with condenser and resistance determine their frequency by a current or potential value in conjunction witha condenser. They Iare well protected against errors inV phase but are greatly dependent,v on operating potentials and currents, and Aaccordingly also on the tubes. They must, therefore, usually be operated by: accumulators and are very sensitive to iiuctuations in the potential of the mains.

(2) Systemsuwith normal oscillatory circuit CL are in the frequency extremely independent of mains potentials and tubes, but are liable to the phase error according to Figs. la, 1b. i

The fundamental idea of the invention set forth in the following consists in producing the synchronisation Vsensitivity fordthe controlled sys tem only during a short fraction of the -controlled oscillation, viz., during a period of the control oscillation, i. e., only during the time Designation: n Shortening SPOIISS- Y A, In Fig. `le there is shown an ideal response curve for a system of the kind in question. The

of Vthe, period of rethe frequency error, which would consistin dis- A placement of the period duration kT2 ofthe controlled oscillation to the Value In this connection there is employed the second fundamental idea according to the invention: e

The controlled system is built up as reactioncoupled oscillator, and inthe reaction-coupling channel there is includeda conductance which is `controlled in full range by the control oscillation. In this way itis accomplished that the oscillations of the controlled system are capable of existing at all only so far as the synchronisation signals arrive in the correct phase or correct frequency. The controlled system, therefore, in accordance with the invention, is designed as a dependent oscillator.

VThe idea Vaccording 'to the invention accordinglyresides in a combination made up of the shorteningof the period` of `response and the dependent-oscillator. e This idea can jbe realised-in very different Ways. Onelofthemost simple connection systems is that according to F'igxZ. 4There is to be recognised in the iirst place an oscillatory circuit comprising the capacity I and theself-induction 2. This oscillatory circuit is tuned to the slow frequency f2. .Its potential time curve canbe in accordance Lwith Fig.:1b.(sine wave). First there is produced'from'thissimple sineY oscillation an impulse curve accordingtoHFig. 1c. Particularly suitable for thispurpose is a method, the socalled phase shifting, which has already been described by theapplicant on Patent 2,190,504. An vauxiliary coil Sinductively coupled-withthe coil 2 A produces vauf-auxiliary potential, which is Ashifted by 180. LThis is conducted to the first grid aofi/a -hexode 4 direct, i.` e., without phaseV shift.

Onthe other hand the terminal Ipotentialof Vthe oscillatory f circuit is conducted Vto the third grid Ac of the samelhexode byway'oflacphase shifter, which consists of the Aresistance and the condenser. 6. .'Ihe -potentialcf the-third grid "4c is accordingly retarded'by -a `phase slip, Vwhich is adjustable at 5,-6,in`.re1ation to the phase of the rst grid da. These .phase-conditions are lillustrated in Fig. 3.

In Fig. A3a the .potential es at the auxiliary coil 3 `is-at the --sam'e time rthe potential ega at `the-grid 4a. @nfthe other hand, in Fig. 3b, ege is A a potentialwhichis phase-shiftedby Vthe vangle po and at the same time turned by 180, such as reaches the third grid 4c, i. e. ego. A plate current can only flow'when the two grids are simultaneously positive. In Fig. 3c it is to be recognised-when this occurs. Fig. 3caccordingly represents the plate current a dependent on'the time. --In this* case, therefore; by -phase shifting, there has ybeen produced from a 'sine -oscillation according to Fig. 3a a shortening of the time of response, viz., an impulse oscillation according to Fig, 3c. In this way there has been fulfilled the first condition relative to the invention. The angle 1- is so adjusted that the impulse duration becomes Tn is the period of the oscillation circuit I, 2. rIfhere must now be fulfilled the second condition according to the invention: the dependent oscillator. For this purpose there is performed the following: 4The anode circuit of the hexode =li -is reaction-coupled to the grid circuit. For

this Vpurpose-there is employed, for example, the

Ycoil -'I -or any other known kind of reaction cou f-,plng vExperience has shown that the reaction coupling energy merely requires to prevail during the'very brief time of the desired period T2. It is not'necessary Vto introduce reaction coupling .energyjntothe `gridAc-:ircuit for the entireduration Yof -the 1period. -Fundamentally, therefore, .thehexodefcan oscillate in-powerfullfashion, a1- though -only brief current -impulses flow in its plate circuit, i. e.. inthe reaction coil 4'I. In order-to act on these oscillations from the control oscillation a .valve must be providedin the reaction channel. For this purpose there can be'employed in simple fashion the screening grids ,rib and iid. Therescreening grids 4b, 6d receive their 'bias from a `potentiometer v8. This bias is selectedtobe so'low that the oscillations of the system can exist weakly or not at all. oscillations from the control transmitter I0 are conducted-to the screening grids by Way of a condenser 9. ID has the frequency f1=n-f2- It is to be recognised now that the oscillations of are producedand are capable of :being upheld if, land only if, afpositive period of the control voscillations (representedin'Fig-Bd) arrives just at the moment when the two grids 4a and'dc are positive. This means that `the system 4Il attemptsto maintain its oscillations continuously, and in thisconnection must so adjust itself that its transmission phase'alWays coincides lwith a positive half-wave of the control oscillation. A ,jumping about in an adjacent period is prevented .by .the-method .of shortened time of vresponse, and a `jumping about in anincorrect'nat.- ural wavelength is 'prevented by the fact that the oscillations of the controlled system must cease if they do not coincide with `a Sub-.harmonic f1. In Fig. 3 there areshown the .conditions withrespect-to a frequency divisionof 1:6.

Numerous modifications of the connection sys- `ternin Fig. 2 are `conceivable without departing from the idea according to the invention. The .supply vof the control potential cangtake place inductively instead of capacitatively, therebeing included'va transformer inplace ,of the working ,resistance Ii I The system according to `1I'ig..2 supplies at the rrr-resistance I2@ potential impulses of Y'negative sign on'the lines of Fig. 23C. Ifit is desired to obtain sine oscillations, there can `be .included inlplacerof I2 a simple or coupled oscillatory circuit I3, I4, 13a, I4a. ,Itsrimpedance `exerts .noappreciable reaction on vthe-system, as vvthe tube VItis fa screening grid tube. VIn `ltlfiisforrxrof connection the system is suitable for the .buildingfup of cascades; a sine oscillation of the .frequency jfl 'is Vintroducedjat I0, Aand ya like oscillation of the reduced frequency fz is obtained at Illa. dAt thisfterminaL therefore, there can 'readily be connected a-further divider system, which is connected in exactly the same manner as that described. Figure 4 shows cascades of these frequency dividers connected in series and very high divider factors brought about. This is of particular importance in television in obtaining a large number of lines. For example 441 is equal to 7 -7-3-3, and consists, therefore, of four dividers in the described `connection with the stated single prime factors. Naturally there can be employed for -coupling and transmission purposes in place of the switching elements also tubes, and preferably screening grid tubes, with which there can be obtained complete freedom from reaction and at the same time considerable sensitivity. Measures of this kind are quite well known to the skilled man. There can also be included an RC system in place of the LC system as shown. Finally, the hexode can be replaced in equivalent fashion by a trode, without the operation of the whole differing from the behaviour set forth in Figs. 1 and 3.

What I claim as new and desire to secure by Letters Patent is: fr

1. A frequency divider comprising a source of high frequency oscillations, a circuit tuned to a subharmonic of said high frequency, means to cause oscillations to take place in said tuned circuit at its tuned frequency, means to transform the oscillations of said circuit into impulses of a duration being substantially equal to one period of said high frequency oscillations, impulse control means to cause the arising of said impulses, only when an oscillation of said high frequency is applied to said impulse control means, and means to excite said tuned circuit by said irnpulses.

2. A frequency divider comprising a source of high frequency oscillations, a circuit tuned to a subharmonic of said high frequency, means including a tube having cathode, at least two grids and an anode `for causing oscillations to take place in said tuned circuit at its frequency, means to transform the oscillations of said circuit into impulses of a duration being substantially equal to one period of said high frequency oscillations, including said tube, means for applying high frequency oscillations to one of said grids and said impulses to the other of said grids, an output circuit between said anode and said cathode, means for coupling said tuned circuit to said output circuit.

3. A frequency divider comprising a source of high frequency oscillations, a circuit tuned to a subharmonic of said high frequency, a tube having a cathode, at least three grids, an anode and an output circuit between said cathode and said anode, means for applying the oscillations of said tuned circuit on the one hand between the cathode and one of said grids and on the other hand between the cathode and another grid in nearly opposite phase so that an impulse of substantially the width of a high frequency oscillation appears in said output circuit, means for applying said high frequency between said cathode and a third grid so that only when an oscillation of said high frequency is applied an impulse can arise, the output circuit of said tube being backcoupled to said tuned circuit.

4. A frequency divider comprising a tube having a cathode, three grids and an anode, means for applying high frequency oscillations to one of said grids, a circuit tuned to a subharmonic of said high frequency connected between a second of said grid and said cathode, and phase shifting means between said second grid and said tuned circuit, an output circuit between said anode and said cathode and a circuit between said third grid and said cathode, means for coupling said tuned circuit to said output circuit and to said third grid circuit, said phase shifting means being proportioned so that the phases of the subharmonic voltages on the second and third grid are sufficiently less than out of phase so that an impulse of substantially the width of a high frequency impulse appears in said output circuit at subharmonic frequency intervals.

5. A frequency divider consisting of a source of high frequency oscillations and a multiple of frequency dividing stages coupling circuits, each stage having input and output and comprising a circuit tuned to a subharmonic of said high frequency, means to cause oscillations to take place in said tuned circuit at its frequency, means to transform said oscillations into impulses of a duration being substantially equal to one period of said high frequency oscillations, impulse control means to cause the arising of said impulses, only when an oscillation of said high frequency is applied to said impulse control means, and means to excite said tuned circuit by said impulses, the input of the second and following of said stages being coupled to the output of each preceding stage via one of said coupling circuits forming the impulses in the output circuit of each stage into sinusoidal oscillations.

KURT SCHLESINGER. 

